Parkinson's disease is a neurodegenerative disorder that is pathologically characterized by the presence of intracytoplasmic Lewy bodies (Lewy in Handbuch der Neurologie, M. Lewandowski, ed., Springer, Berlin, pp. 920-933, 1912; Pollanen et al., J. Neuropath. Exp. Neurol. 52:183-191, 1993), the major components of which are filaments consisting of α-synuclein (Spillantini et al., Proc. Natl. Acad. Sci. USA 95:6469-6473, 1998; Arai et al., Neurosci. Lett. 259:83-86, 1999), a 140-amino acid protein (Ueda et al., Proc. Natl. Acad. Sci. USA 90:11282-11286, 1993). Two dominant mutations in α-synuclein causing familial early onset Parkinson's disease have been described, suggesting that Lewy bodies contribute mechanistically to the degeneration of neurons in Parkinson's disease and related disorders (Polymeropoulos et al., Science 276:2045-2047, 1997; Kruger et al., Nature Genet. 18:106-108, 1998; Zarranz et al., Ann Neurol. 55:164-173, 2004). Triplication and duplication mutations of the α-synuclein gene have been linked to early-onset of Parkinson's disease (Singleton et al., Science 302:841, 2003; Chartier-Harlin at al. Lancet 364:1167-1169, 2004; Ibanez et al., Lancet 364:1169-1171, 2004). In vitro studies have demonstrated that recombinant α-synuclein can indeed form Lewy body-like fibrils (Conway et al., Nature Med. 4:1318-1320, 1998; Hashimoto et al., Brain Res. 799:301-306, 1998; Nahri et al., J. Biol. Chem. 274:9843-9846, 1999). Both Parkinson's disease-linked α-synuclein mutations accelerate this aggregation process, demonstrating that such in vitro studies may have relevance for Parkinson's disease pathogenesis. α-Synuclein aggregation and fibril formation fulfill the criteria of a nucleation-dependent polymerization process (Wood et al., J. Biol. Chem. 274:19509-19512, 1999).